Time-resolved infrared studies of metal carbonyl complexes

Wu, Lingjun (2020) Time-resolved infrared studies of metal carbonyl complexes. PhD thesis, University of Nottingham.

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Chapter 1 Introduction

A brief overview of time-resolved Infrared (TRIR) spectroscopy is given in this Chapter. This technique has been used throughout this thesis to investigate the role of transient intermediates aiding in the elucidation of reaction mechanisms.

Chapter 2 TRIR Investigations on E-H (E: Si, Ge, Sn) Bond Activation by (h5-C5HnMe5-n)M(CO)3 Complexes (M= Mn, Re) – towards Time-Resolved XAFS Studies

The E-H (E: Si, Ge, Sn) bond activation of HEBu3 by the (h5-C5HnMe5-n)M(CO)3 complexes (M= Mn, Re) has been investigated in two solvents, n-heptane and perfluoromethylcyclohexane (PFMCH), in order to support future time-resolvedXAFS (TR-XAFS) investigations. In heptane upon UV photolysis, (h5-C5HnMe5n)M(CO)3 undergoes CO-loss to form the dicarbonyl species (h5-C5HnMe5-n)M(CO)2, which is quickly solvated to form (h5-C5HnMe5-n)M(CO)2(n-heptane). Triplet dicarbonyl species 3CpMn(CO)2 and 3Cp’Mn(CO)2 were also observed. The (h5C5HnMe5-n)M(CO)2(n-heptane) complex undergoes substitution by HEBu3. However, this ligand exchange does not occur for CpRe(CO)3 in n-heptane, which is attributed to the extremely strong interaction between Re and n-heptane. The E-H bonds were found to undergo more complete activation with the Re complexes, and it was also found that the addition of electron rich substituents onto the Cp ring can facilitate oxidative addition. The overall interaction with the metal centers follow the order: Sn > Ge > Si. While the p-backbonding interaction between Mn and E-H follows: Ge ≥ Si > Sn. In PFMCH, it is found the coordination of the E-H bond to the metal complexes is much faster than in heptane, which is attributed to the weak coordinating property of PFMCH. In PFMCH, ligand exchange within the same HEBu3 molecule is observed and this mechanism is supported by the kinetics.

Chapter 3 TRIR Investigations on the Photochemistry and Photophysics of Tungsten Carbonyl Complexes

In this Chapter, the results of TRIR investigations on the photoproperties of W(CO)6 and a series of its derivatives, the W(CO)5L complexes (L: pyridine, piperidine, 4acetylpyridine) are described. Particularly the rate of E-H (E: Si, Ge, Sn) bond activation has been investigated. Upon UV photolysis, W(CO)6 loses one CO to form W(CO)5, which undergoes fast solvation in heptane to form W(CO)5(n-heptane). In the presence of the dopant HEBu3 (E: Si, Ge, Sn), ligand exchange occurs to form W(CO)5(HEBu3). It is proposed that the E-H bond may coordinate to the W centre in an h1-fashion. This is supported by TR-XAFS studies conducted by our collaborators.

Interactions with halocarbons were also investigated using TRIR. X-cyclohexane (X: Cl, Br) are found to coordinate to the W centre via the halogen lone pair. For benzene and F-benzene, a “ring-edge” binding mode is observed, in which the W centre coordinates to the C=C bond. For F-benzene and Cl-benzene, an unstable intermediate W(CO)5(CH=CXC4H4) (X: F, Cl) is observed, which converts to the final stable product. For F-benzene, the final product is the “ring-edge”-bound species W(CO)5(CH=CHC4H3F). The W(CO)5(h1-X-Ph) (X: Cl, Br, I) species were observed for Cl-benzene, Br-benzene and I-benzene as the final stable product. For Brbenzene and I-benzene, the partially oxidized product [W(CO)5(X---phenyl)] (X: Br, I) was observed, in which a 3-c-2-e interaction between W and C-X is proposed.

The W-Xe interaction for the W(CO)5L (L: pyridine, piperidine, 4-acetylpyridine) complexes has also been explored using TRIR. The Xe species W(CO)5Xe forms in PFMCH in the presence of Xe upon UV photolysis. This observation is supported by TR-XAFS studies conducted by our collaborators.

Chapter 4 Photophysics Studies on Re-diimine Complexes

The photophysics of the [Re(CO)3(dppz-NPh2)Cl] complex (dppz: dipyrido[3,2-a: 2’3’-c]phenazine) in different solvents (toluene and acetone) and the [Re(CO)3(Phen-TPA)X]n=0,1 (X: Cl-, Br- n=0; py (pyridine), dmap (4(dimethylamino)pyridine) n=1; phen: 1,10-phenanthroline; TPA: triphenylamine) complexes in CH2Cl2 have been investigated using TRIR. For the [Re(CO)3(dppzNPh2)Cl] complex, three excited states with different lifetimes based on the dppzNPh2 ligand are observed, denoted as states I, II and III. Upon UV photolysis, state I and III are formed, and state I converts to state II on the ps timescale, while state III decays to the ground state. State II is observed to be stable with a lifetime of several µs. It is found that the lifetime of state III is prolonged in acetone compared to that observed in toluene, while changing the solvent has little impact on the lifetimes of state I and II. It is also found that the lifetimes of state II and III are highly dependent on the concentration of [Re(CO)3(dppz-NPh2)Cl], while the lifetime of state I is nearly unaffected. For the Re-phen complexes [Re(CO)3(PhenTPA)X]n=0,1 (X: Cl-, Br- n=0; py, dmap n=1), a conversion between the 1ILCTTPA®phen and 3ILCTTPA®phen states (ILCT: intraligand charge transfer) is observed. The lifetime of the 3ILCT state for [Re(CO)3(Phen-TPA)L]+ (L: py, dmap) is ca. 20-30 ns, while the lifetime for the halide complexes [Re(CO)3(Phen-TPA)X] (X: Cl-, Br-) is much longer, for ca. 2.0-3.0 µs. This can be explained by the energy gap law.

Chapter 5 TRIR Investigations on the Photoproperties of MOF Materials

This Chapter details the TRIR investigations of two MOF materials, Re-MOF and MnMOF, as well as their linker complexes. DFT calculations have also been undertaken to aid in assignment of the mechanisms. Upon UV photolysis of the linker complex of the Re-MOF, Re(CO)3(bdmpzm)Cl, a pp* excited state and the solvated dicarbonyl species Re(CO)2(bdmpzm)Cl(solvent) are observed to form. The pp* excited state decays in ca. 60 ps to the ground state, while the solvated species Re(CO)2(bdmpzm)Cl(solvent) was found to be stable and shows no decay during the experimental timescale. When incorporated into a MOF scaffold, the pp* excited state and the solvated species Re(CO)2(bdmpzm)Cl(solvent) are also observed. However, at later timedelays, after the decay of both the pp* excited state and Re(CO)2(bdmpzm)Cl(solvent), an excited state in the MOF scaffold is observed.

For the Mn linker complex Mn(CO)3(bdmpzm)Br, upon UV photolysis, unsaturated dicarbonyl species Mn(CO)2(bdmpzm)Br in both fac- and mer-configurations are observed, which then coordinate to solvent molecules. The solvated species Mn(CO)2(bdmpzm)Br(solvent) undergoes a structural isomerization to a more stable configuration. When incorporated into a MOF scaffold, similar reaction processes were apparent. Finally, different solvents in the MOF channel were investigated.

Chapter 6 Experimental

All the experimental techniques, methods and sample preparations are described in this Chapter

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: George, Michael
Keywords: Reaction mechanisms, E-H (E: Si, Ge, Sn) bond activation, Halocarbons, Re-diimine complexes, Time-resolved infrared.
Subjects: Q Science > QD Chemistry
Faculties/Schools: UK Campuses > Faculty of Science > School of Chemistry
Item ID: 56771
Depositing User: Wu, Lingjun
Date Deposited: 27 Aug 2020 13:05
Last Modified: 27 Aug 2020 13:15
URI: http://eprints.nottingham.ac.uk/id/eprint/56771

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